1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having improved electrophotographic characteristics.
2. Related Background Art
In recent year, an electrophotographic photosensitive member of a function-separation type, which comprises separate substances having respectively a charge-generating function and a charge-transporting function, brought about remarkable improvements in sensitivity and durability which had been disadvantages of conventional organic photosensitive members.
Such function-separation type of electrophotographic photosensitive members are advantageous because the substances for the charge-generating material and the charge-transporting material can each be selected from a wide variety of substances, which allows production of an electrophotographic photosensitive member having desired properties relatively easily at low cost.
Various compounds serving charge-transporting function are reported as the charge-transporting substances, including hydrazones as disclosed in U.S. Pat. No. 4,150,987, triazoles and pyrazolines as disclosed in U.S. Pat. No. 3,837,851, stilbenes as disclosed Japanese Patent Laid-Open Application No. 58-198043, benzidines as disclosed in Japanese Patent Laid-Open Application Nos. 61-295558 and 62-201447, and so forth.
One of the characteristics required for charge-transporting substances is resistance to deterioration caused by ozone and NOx produced by corona discharge, and light illumination.
A new problem resulting from recent improvements in durability of photosensitive members and in quality of images is the memory-resting phenomenon. This phenomenon is, in principle, deterioration caused by substances produced by corona discharge, resulting in decrease of chargeability, when the rotation of a sensitive member stops after completion of copying in the vicinity of a corona charger. This leads to decrease of image density in positive development or increase of image density in reversal development at that portion which stops near the corona charger. This phenomenon tends to occur after long time use of the photosensitive member, and is becoming a more and more serious problem with lengthening the life of photosensitive members.